ISO-8601 in Postgres: How to insert only year in type date? (incomplete date-time values)

Question

The Postgres database claims it supports the ISO-8601 standard. In ISO-8601 a date format \"yyyy\", i.e. consisting of only the year, is fine and acceptable. But I can\'t find a

Answer 1

To get the year of a date data type:

select extract(year from '2014-01-01'::date) as the_year;
 the_year 
----------
     2014

If you only need the year then use a smallint with a check constraint

create table t (
    the_year smallint check(
        the_year between 0 and extract(year from current_date)
    )
);

insert into t (the_year) values (2030);
ERROR:  new row for relation "t" violates check constraint "t_the_year_check"
DETAIL:  Failing row contains (2030).

insert into t (the_year) values (2014);
INSERT 0 1

But if you will store the whole date then it makes no sense to separate into 3 columns.

Note that the semantics of the column are up to the application. If a column is of the date type but the application only considers the year then that column means the year.

Check the Date/Time Functions and Operators

---

One solution to the partial date problem pointed by @a_horse in the comments is to create a column indicating the precision of that date

create table t (
    the_date date,
    the_date_precision varchar(5)
);

insert into t (the_date, the_date_precision) values
(current_date, 'year'),
(current_date, 'month'),
(current_date, 'day')
;

select
    case the_date_precision
        when 'year' then to_char(the_date, 'YYYY')
        when 'month' then to_char(the_date, 'YYYY-MM')
        else to_char(the_date, 'YYYY-MM-DD')
    end as the_date
from t
;
  the_date  
------------
 2014
 2014-02
 2014-02-06

The above is the KISS aproach but I think the next implementation is more elegant

create table t (
    the_date date,
    the_date_precision smallint
);

insert into t (the_date, the_date_precision) values
(current_date, 1),
(current_date, 2),
(current_date, 3)
;

select
    array_to_string(
        (
            string_to_array(to_char(the_date, 'YYYY-MM-DD'), '-')
        )[1:the_date_precision]
        , '-'
    ) as the_date
from t
;
  the_date  
------------
 2014
 2014-02
 2014-02-06

That select expression could be turned into a function to be easier to reproduce. Or just a view

create view view_t as 
select *,
    array_to_string(
        (
            string_to_array(to_char(the_date, 'YYYY-MM-DD'), '-')
        )[1:the_date_precision]
        , '-'
    ) as the_date_output
from t
;
select * from view_t;
  the_date  | the_date_precision | the_date_output 
------------+--------------------+-----------------
 2014-02-06 |                  1 | 2014
 2014-02-06 |                  2 | 2014-02
 2014-02-06 |                  3 | 2014-02-06